Powder metallurgy is a common manufacturing method used to produce components of high quality for applications such as engines. Powder metallurgy is often employed in the manufacture of engine components because it is economical, flexible, and can produce a finished part that requires less machining or secondary processing than other methods of forming components. Powder metallurgy allows for a component to be formed of a wide variety of alloys, composites, and other materials to provide the finished component with desirable characteristics. Powder metallurgy is well suited to manufacture parts of a wide range of sizes and shapes. Also, powder metallurgy can reliably produce parts with consistent dimensions and advantageous physical properties.
Referring to FIG. 1, a process chart for the conventional powder metallurgical component forming process 30 is shown. First, the metal powders 32 that comprise the component are provided. Often, lubricants are added to the metal powders to decrease the wear of pressing machinery. Next, the base powders are mixed 34 to form a homogenous mixture. The finished part is ultimately a homogeneous alloy of the constituent metal powders.
A mold or die is then filled 36 with the mixed powders. The die, when closed, has an internal cavity somewhat similar in shape to the final part. The powder is compressed 38 within the die to form a so-called “green part.” The compaction 38 is usually performed at room temperature and at pressures, for example, in the range of 30-50 tons per square inch. The green part, also referred to as a “green compact,” has the desired size and shape for the next operation when ejected from the die. After compaction 38, the green part has sufficient strength for further processing.
The green part is subjected to a sintering process 40. A variety of secondary operations 42 may be performed on the part after sintering 40, depending on its intended use, the process yielding a finished part 44.
Generally, sintering 40 involves subjecting the green part to a temperature, for example, of 70-90% of the melting point of the metal or alloy comprising the green part. The variables of temperature, time, and atmosphere are controlled in the furnace to produce a sintered part having improved strength due to bonding or alloying of the metal particles. The sintering process 40 generally comprises three basic steps conducted in a sintering furnace: burnoff 46, sinter 48, and cooling 50. Continuous-type sintering furnaces are commonly used to perform these steps. The burnoff chamber is used to volatize the lubricants used in forming green part 46. The high-temperature chamber performs the actual sintering 48. The cooling chamber cools the sintered part prior to handling 50.
The parts that exit the sintering furnace 40 after cooling 50 may be considered complete. Alternatively, they may undergo one or more secondary operations 42. Secondary operations include, for example, re-pressing (forging) the component 52, machining 54, tumbling 56, and joining the component with additional components 58 as part of an overall assembly. The secondary operations 42 may also include the impregnation of oils or lubricants 60 into the part for conveying self-lubricating properties. The sintered component may also undergo heat treatment 62 to provide certain characteristics and properties to the component, such as strength. Those skilled in the art will recognize that other secondary operations may be performed. The secondary operations 42 may be performed individually or in combination with other secondary operations. Once all the secondary operations 42 are performed, the component or part 44 is finished.
U.S. Pat. Nos. 6,055,884, 5,551,782, and 5,353,500 each disclose connecting rods for use in an internal combustion engine.
FIG. 2 illustrates the internal detail of a conventional internal combustion engine to illustrate the use of a connecting rod 64. Connecting rod 64 is pivotally connected to a piston 66 and the crankshaft 74. The connecting rod 64 is connected to the crankshaft 74 at a large or crank end 76. The large end 76 of the rod 64 receives a shaft portion (“crank pin”) 78 of the crankshaft 74. The connecting rod 64 is further connected to a piston 66 at a small or piston end 70 of the rod 64. A pin (“wrist pin”) 68 is used to permit rotation between the small end 70 of the connecting rod 64 and the piston 66.
Referring to FIG. 3 through FIG. 5, a conventional connecting rod 64, manufactured according to conventional methods is shown. Connecting rod 64 comprises a piston end 70, a crankshaft end 76, and a shank 80. The shank 80 is often provided with one or more recesses 82 for weight savings. Crankshaft end 76 includes a large eye 77 for receiving the crank pin 78. Crankshaft end 76 includes a crank bearing 84 for minimizing wear and friction due to the rotational movement of shaft 78 within large eye 77. The bearing 84 comprises bearing material 88, an outer material seating surface 89 and an inner bearing surface 86. Those of skill in the art will recognize that the crank bearing 84 forms a hydrodynamic bearing when lubricating oil is provided between the crank pin 78 and the inner bearing surface 86.
The piston end 70 of connecting rod 64 includes a small eye 81 for receiving wrist pin 68. Small eye 81 is provided with a bushing 90 for reducing friction and wear due to rotational motion in operation. Bushing 90 comprises discrete or separate bearing material 92, an inner bearing contact surface 94, and an outer bearing seating surface 96.
A connecting rod 64 is ordinary comprised of a steel or aluminum alloy. Titanium alloys are now also used for connecting rods 64. The bushing 90 is typically comprised of bronze.
The crank bearing 84 and bushing 90 are conventionally provided to connecting rod 64 as part of a secondary manufacturing and assembly process. Each bearing 84 and bushing 90 are typically formed as part of its own separate manufacturing process and then joined with the connecting rod 64 as a separate manufacturing or assembly step. The additional steps add time, tooling, and labor costs to the manufacturing process. A continuing goal of all manufacturing is to reduce costs.
Therefore, there remains a need to provide connecting rods for engines that have a reduced number of manufacturing steps, tooling, parts, and labor.